Tie rod for a strip-type tension member, used in the building trade

ABSTRACT

The invention relates to a tie rod for a strip-type tension member ( 1 ), used in the building trade, and consisting especially of fibre-reinforced plastic lamellae. Said tie rod comprises at least one anchoring body ( 2 ) which is positively connected to the tension member ( 1 ) by means of adhesion and/or friction, and can be supported on a fixed abutment. The anchoring body ( 2 ) comprises a plurality of clamping blocks ( 3 ) which are arranged at a distance from each other in the longitudinal direction of the tension member and are connected to said tension member ( 1 ) by means of adhesion and/or friction. One of said clamping blocks is supported on the fixed abutment ( 7 ), and the clamping blocks are interconnected by extension sections ( 9 ) having different spring stiffnesses, the spring stiffnesses of said extension sections ( 9 ) increasing towards the end of the tension member ( 1 ). The extension sections ( 9 ) are embodied as connecting pieces having different cross-sections or recesses, or can consist of materials having different elasticity modules.

BACKGROUND OF THE INVENTION

[0001] The invention relates to a tie rod (tie anchor) for strip-typetension members used in the building trade, especially fiber-reinforcedplastic lamellae having at least one anchoring body positively connectedto the tension member by means of adhesion and/or friction whereby saidanchoring body can be supported on a fixed abutment.

[0002] It is known in the art to attach pretensioned strip-type tensionmembers on the outside of the supporting framework after erection toincrease the load capacity (strengthening) or to restore the originalload capacity (reconstruction) of supporting frameworks made ofreinforced concrete or prestressed concrete. Fiber-reinforced plasticlamellae are preferably used for this purpose aside of steel lamellae(bands), especially synthetic materials reinforced with carbon fibers,synthetic materials reinforced with aramide, and synthetic materialsreinforced with glass fibers.

[0003] A significant characteristic of these fiber-reinforced syntheticmaterials, in particular the preferably employed synthetic materialsreinforced with carbon fibers, is the fact that the strip-type tensionmembers made from these materials show linear elastic behavior up to thebreaking point. Attention must be given in the necessary anchoring ofthe end pieces of the tension members to maintain single-axis tensilestress conditions. A dual-axis tensile stress condition caused bysubstantial stress spikes at the clamping point and/or at the point ofdeflection would lead to damage or even to destruction of the strip-typetension member.

[0004] The transition point from the free span length of the tensionmember to the anchoring zone is non-uniform in terms of stiffness,specifically at the adhesive attachment of the strip-type tension memberto the anchoring bodies. A spike in shearing stress occurs at thetransition from free span length to the anchoring zone since theadhesive length which can be activated is relatively short and whichabsorbs the load initiated by the tension member through shearing stresswhereby said spike in shearing stress exceeds the locally admissibleshearing stress in the adhesive joint and reaches the ultimate stress(breaking stress). The crucial breaking criteria in case of the use ofan adhesive is hereby the exceeding of cohesion of the adhesive and/orthe breaking of the plastic matrix of the strip-type tension member. Thethereby formed breaking shear-stress front moves along the adhesivejoint until the adhesive connection breaks down completely.

[0005] It is know from prior art (DE 198 49 605 A1 and corresponding toU.S. Pat. No. 6,584,738) to apply an additional clamping force betweenthe anchoring body and the tension member glued thereto to increase theadhesive effect. The thereby developing dual-axis stress condition(longitudinal stress/limited transverse pressure) is harmless for thetension member since no transverse stress occurs. There occurs rather anincrease of the crucial breaking strength. However, the spike inshearing stress is thereby not decreased at the transition from the freespan length to the anchoring zone.

[0006] For the solution of the problem of decreasing or of avoiding aspike in shearing stress at the transition from the free span lengthinto the anchoring zone, it has been proposed in prior art to alter theadhesive characteristics along the force introduction area in such amanner whereby a relatively soft adhesive is used at the transition tothe anchoring (less shear modulus) and the adhesive characteristics onthe other end of the anchoring is altered in such a way that theadhesive is provided with a high shear modulus and whereby the adhesiveacts substantially stiffer. However, the selection of adhesive materialand especially the maintaining of set conditions in the application ofthe adhesive demand very high requirements and they are notcontrollable, especially after application.

[0007] It is also known from prior art to embed a perforated metal plateor similar material in the adhesive joint. A generally lower shearmodulus of the adhesive joint is achieved thereby without reducing thetotal load capacity. The damaging spike in shearing stress can,nevertheless, be reduced thereby—but not to a sufficient degree in manycases of application.

[0008] It is therefore the object of the invention to design a tie rodof the aforementioned type in such a manner that the development of aspike in shearing stress is avoided which locally exceeds the ultimatestress in the adhesive joint or in the region of friction.

SUMMARY OF THE INVENTION

[0009] This object is achieved according to the invention in that theanchor body is provided with a plurality of clamping blocks, which arearranged at a distance from each other in longitudinal direction of thetension member and which are connected to said tension member by meansof adhesion and/or friction whereby the last clamping block toward theend of the tension member can be supported on the fixed abutment,whereby the clamping blocks are interconnected by extension sectionshaving different degrees of spring stiffnesses, and whereby the springstiffnesses of said extension sections increase toward the end of thetension member.

[0010] Achieved is thereby, nevertheless, a stepped but stillsufficiently uniform declining gradient of the transferred tensile forcein the adhesive joint or in the region of friction from the transitionof the free span length to the anchoring. The shearing stress is reducedup to the transition into the free span length of the tension member tosuch a degree that neither the cohesion of the adhesive nor the maximalpossible friction force is exceeded at this point or that damage occursto the tension member itself.

[0011] According to a preferred embodiment of the invention, it isproposed that an anchoring body is arranged on both sides of astrip-type tension member or on a layer of two strip-type tensionmembers whereby the clamping blocks of said anchoring body stacked ontop of one another are connected to each other by means of clampingelements. The clamping elements are preferably tension bolts arranged atboth sides adjacent to the tension member. The varying elastic extensionsections, which means, extension sections designed having differentspring stiffnesses, are made constructively very simple and can bemanufactured in a simple manner as connecting pieces having differentcross sections. The different cross sections of the connecting pieces,which can be produced in several ways as described below, lead tovarying spring stiffnesses. The requirement of designing the springstiffness of the extension sections to increase toward the end of thetension member can be realized thereby in a very simple manner.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Embodiment examples of the invention, which are illustrated inthe drawings, are explained in more detail in the following:

[0013]FIG. 1 shows in a longitudinal section a highly schematicillustration of a tie rod for a strip-type tension member whereby springsymbols are used for the extension sections of varying spring stiffness;

[0014]FIG. 2 shows a top view onto the schematically illustrated tie rodin FIG. 1;

[0015]FIG. 3 shows a top view onto an embodiment example of a tie rodfor a strip-type tension member;

[0016]FIG. 4 shows a side view of the tie rod in FIG. 3 whereby thesupport on a fixed abutment is not shown for the sake of clearerillustration;

[0017]FIG. 5 shows a spatial illustration of the tie rod in FIG. 4;

[0018]FIG. 6 shows a top view onto a tie rod according to the firstembodiment;

[0019]FIG. 7 shows a sectional view along line VII-VII in FIG. 6;

[0020]FIG. 8 through FIG. 12 show additional embodiment examples inillustrations according to FIG. 6 and FIG. 7.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0021] The basic design of a tie rod for a strip-type tension member 1,consisting of lamellae made of synthetic material reinforced with carbonfibers, is explained with the aid of FIG. 1 and FIG. 2. These strip-typetension members 1 are employed in the building trade for strengtheningor reconstruction of supporting frameworks made of prestressed concreteor reinforced concrete. The strip-type tension members are attached ontothe concrete surface through adhesion, for example, or are placed on theconcrete surface without any bonding material. The described tie rodsserve to create prestress and/or terminal anchoring for tension members.

[0022] An anchoring body 2 is bonded hereby to the tension member 1through adhesion and clamping. Instead, bonding can also be achievedthrough friction. The adhesive bond is described in the following as oneof the possible embodiment examples. The anchoring body 2 is providedwith a plurality of clamping blocks 3 arranged at a distance from eachother in longitudinal direction of the tension member 1. Each of theclamping blocks 3 is connected to the tension member 1 by adhesionthrough an adhesive layer 4. Each clamping block is connected to aclamping counterpiece 6 by means of clamping bolts 5, which areindicated only schematically in FIG. 1. Said clamping counterpieces 6can, in turn, be parts of a second clamping body 2 at the bottom of thetension member 1.

[0023] The last clamping block 3 toward the end of the tension member,which is the clamping block 3 arranged to the very left in theillustrated embodiment example, is supported by connectors 8 on a fixedabutment 7 attached to the supporting frame via a hydraulic tensioningdevice, for example.

[0024] Extension sections 9 are provided between the individual clampingblocks 2 whereby said extension sections are symbolized as groups ofsprings in the illustration of FIG. 1 and FIG. 2. The varying thicknessof the tension springs show that the extension sections 9 are designedhaving different spring stiffnesses whereby the spring stiffnessincreases from the transition point 10 of the free span length of thetension member 1 into the anchoring zone toward the end of the tensionmember (left in FIG. 1 and FIG. 2).

[0025] The spring stiffnesses of the extension sections 9 are therebyselected and graduated (stepped) in such a manner that forceintroduction in each clamping block 3 occurs through shearing stress inthe adhesive layer 4, which prevents the development of spikes inshearing stress that exceed the maximum admissible shearing stress inthe adhesive and which would lead to a breakdown of cohesion. Adhesioncan also occur in the area of the extension sections 9, deviating fromthe embodiments illustrated in the drawings.

[0026] The varying spring stiffness of the extension sections 9 can beconstructively achieved in various ways; preferred examples are herebyillustrated in the following drawings.

[0027] In the embodiment example of a tie rod for tension members 1illustrated in FIG. 3 through FIG. 5, consisting of plastic lamellaereinforced with carbon fibers, for example, there is arranged ananchoring body 2 at both sides of a layer of two strip-type tensionmembers 1 whereby its clamping blocks 3 disposed on top of each otherare interconnected and clamped by means of tension bolts 5 that arerespectively arranged laterally adjacent to the tension member 1 instraddling relationship thereto. For the purpose of uniform forceintroduction, the tension bolts 5 bias the respective clamping blocks 3through a transverse connecting piece 12 and through two juxtaposedsupport areas 11 a and 11 b. A single central support area can also beselected in place thereof. A plurality of individually functioningidentical tie rods can be combined by stacking on top of one another asa modulus to a larger tension member whereby longer common tension bolts5 are used.

[0028] The last clamping block 3 toward the end of the tension member 1is connected to an end plate 2 a of the anchoring body 2. Said end plate2 a is supported on the fixed abutment 7 via lateral hydraulictensioning cylinders 8.

[0029] The extension sections 9 between the clamping blocks 3 are formedby connecting pieces 13, which are uniform in width but are of varyingthickness. The thickness of the connecting pieces increases from thetransition point 10 toward the end plate 2 a, and thus toward the end ofthe tension member 1.

[0030]FIG. 6 shows in a top view and in a simplified manner ofillustration the basic design of the anchoring body 2 as it is used inthe embodiment example according to FIG. 3 through FIG. 5. Additionalembodiment examples are illustrated in FIG. 8 through FIG. 15 in thesame manner of illustration.

[0031] In the example according to FIG. 8 and FIG. 9, the connectingpieces forming the extension sections 9 between the clamping blocks 3consist respectively of a plurality of connecting sections 14, which areseparated from each other by recesses, and of borings 15 runningperpendicular relative to the strip-type tension member 1. Therespective entire connection cross section of all connecting sections 14of the individual extension sections 9 are all different from oneanother. As it is shown in FIG. 8 and FIG. 9, the borings 15 in theextension section 9 disposed closest to the transition point 10 have thelargest diameter so that the entire connection cross section of allconnecting sections 14 is here the smallest. The diameters of the boring15 are smaller in the subsequent extension section 9 and the entirecross section of the connecting piece is thereby larger. Finally, thediameters of the borings 15 in the extension section 9 next to the endof the transition member 1 are even smaller and the entire cross sectionof the connecting piece is larger.

[0032] The embodiment example in FIG. 10 and FIG. 11 differs from theafore-described embodiment example substantially by the fact that theborings 15′ separating the connecting sections 14′ of each extensionsection 9 run parallel to the surface of the strip-type tension member 1and transverse (orthogonally) to the longitudinal direction of thestrip. Each boring 15′ separates from each other two connecting sections14′ within each extension section 9. The diameter of the borings 15′decrease here also starting from the transition point 10 while theentire cross section of the connection sections 14′ increases.

[0033] In the embodiment example in FIG. 12 and FIG. 13, a bendingsection 16 is formed in each extension section 9 oriented transverse(orthogonally) to the longitudinal direction of the tension member 1.The bending sections of the individual extension sections 9 havedifferent degrees of flexural strength.

[0034] The bending sections 16 or bending beams are placed in a slot 17which extends into the anchoring body 2 between the two opposing sidesof the tension member.

[0035] The decreasing depth of the slot 17 starting from the transitionpoint 10 receives the effective length of the bending section 16. Theincreasing space in the respective neighboring slots 17, starting fromthe transition point 10, is reached at the same time so that thethickness of the bending sections 16 increases. Both measures, usableindividually or in combination, lead to the fact that the springstiffness of the bending sections 16 increases starting from thetransition point 10 and continues toward the end of the tension member1.

[0036] In the embodiment example in FIG. 14 and FIG. 15, the extensionsections 9 between the clamping blocks consist of material of varyingelasticity modulus. The elasticity modulus of the material used for theextension sections 9 increases starting at the transition point 10,which means, the spring stiffnesses of the extension sections 9 increasetoward the end of the tension member 1.

[0037] The stepped gradient of the anchor stiffness with graduation inthe “load transfer zone” by means of bonding material and the “extensionzones” preferably without a bond serve to forward as much tensile forcefrom the lamella to the load introduction zone as can be transferredthrough the selected bonding principle (adhesion+transverse pressure orfriction+transverse pressure) without experiencing any damage. This loadintroduction zone avoids subsequent additional stresses through wideningof the extension zone and the next load transfer zone is then activated.In the ideal situation, each load introduction zone transfers a specificportion of the total tensile force

1-12. (canceled)
 13. A tie anchor for tension members, the tensionmember comprising a strip having opposing sides, the tie anchorcomprising an anchor body disposed on at least one of the strip sidesand including at least first, second, and third clamping blocks arrangedat a distance from one another in a longitudinal direction of the strip,the clamping blocks connected to the one strip side by at least one of:adhesive and friction; wherein the first clamping block constitutes alast clamping block disposed at an anchoring end of the tension memberand is adapted to be supported on a fixed abutment, wherein the secondand third clamping blocks are interconnected by a first extensionsection having a first spring stiffness, and the first and secondclamping blocks are interconnected by a second extension section havinga second spring stiffness greater than the first spring stiffness. 14.The tie anchor according to claim 13 wherein the anchor body constitutesa first anchor body, the tie anchor further including a second anchorbody disposed on the other side of the strip; wherein the first andsecond anchor bodies are interconnected by clamping elements.
 15. Thetie anchor according to claim 14 wherein the clamping elements comprisetension bolts extending through the first and second anchor bodies instraddling relationship to the strip.
 16. The tie anchor according toclaim 13 wherein the extension members comprise respective connectionpieces having different respective cross sectional sizes.
 17. The tieanchor according to claim 16, wherein the connection pieces havesubstantially equal widths and different thicknesses.
 18. The tie anchoraccording to claim 16 wherein the connecting pieces comprise respectiveconnecting sections separated from each other by recesses formed in theanchor body.
 19. The tie anchor according to claim 18, wherein therecesses comprise bores extending perpendicular to the strip.
 20. Thetie anchor according to claim 18, wherein the recesses comprise boresextending orthogonally relative to a longitudinal direction of thestrip.
 21. The tie rod according to claim 13 wherein each extensionsection includes a bending section extending orthogonally relative to alongitudinal direction of the strip, wherein the bending sections ofrespective extension sections have different respective degrees offlexural strength.
 22. The tie rod according to claim 13 wherein eachextension section includes first and second slots extending into theanchor body from respective sides thereof, a portion of each extensionsection disposed between the first and second slots thereof defining abending section.
 23. The tie anchor according to claim 22, wherein thebending sections are of different respective thicknesses.
 24. The tieanchor according to claim 22 wherein the bending sections are ofdifferent respective lengths.
 25. The tie anchor according to claim 13wherein the extension sections comprise respective materials havingdifferent respective modulii of elasticity.
 26. The tie anchor accordingto claim 13 wherein the first clamping block carries connectors forconnecting the anchor body to a fixed abutment.
 27. The tie anchoraccording to claim 13 wherein the strip comprises a fiber-reinforcedplastic lamellae.
 28. A building structure including a fixed abutment, atension member comprising a strip having opposite sides, and a tieanchor interconnecting the strip and the fixed abutment; the tie anchorcomprising an anchor body disposed on at least one of the strip sides,and including a plurality of clamping blocks arranged at a distance fromeach other in a longitudinal direction of the strip; the clamping blocksbeing connected to the one strip side by at least one of: adhesive andfriction; wherein an end-most clamping block is secured to the fixedabutment; adjacent clamping blocks being interconnected by expansionsections, each expansion section defining a spring stiffness, whereinthe respective spring stiffnesses become progressively stronger towardthe end-most clamping block.